Chitosan-Based Thermosensitive Materials

Thermosensitive polymers are materials capable of undergoing a reversible phase transition in aqueous media in response to a variation of the temperature. They have attracted high scientific interest for advanced applications in diverse areas, such as biotechnology, biomedical, environmental, food industry and other fields. At the same time, chitosan is a promising marine polysaccharide that has long been used in applications such as drug, peptide or gene delivery systems. Being the most abundant marine polysaccharide, chitin and chitosan do not exhibit thermoresponsive properties, but some of their derivatives do. In the present chapter, the efforts to produce chitosan-based thermosensitive materials are reviewed. Particularly, the properties and applications of chitosan-glycerophosphate thermogelling system are examined; the methods of synthesis of chitosan copolymers grafted with poly(N-isopropylacrylamide) or poly(N-vinylcaprolactam), their physicochemical properties and most of their prominent applications are discussed as well

Síntesis y caracterización de redes poliméricas interpenetradas de quitosana-poli(ácido acrílico-coacrilamida)

Se prepararon redes poliméricas interpenetradas de quitosana (QUI) con poli(ácido acrílico) (PAAc) y poliacrilamida (PAAm) mediante la polimerización radicálica de la acrilamida (AAm) y el ácido acrílico (AAc) en presencia de la quitosana, utilizando como sistema iniciador persulfato de amonio, [(NH4)2S2O8, a 1,2 · 10-3 mol/L] con N,N,N’,N’- tetrametilendiamina como activador, en relación 1 : 1 mol/L con el persulfato a 50 ºC . Se utilizó como entrecruzante la N,N’-metilenbisacrilamida a 3,3 ·10-3 mol/L . Los materiales obtenidos se caracterizaron por microscopia electrónica de barrido y la composición relativa de los polímeros en los sistemas fue confirmada por espectroscopia FTIR. Se utilizaron la relaciones de absorbancias a 1 670, 1 662 y 1 082 cm–1, A1662/A1082 y A 1670/A1082, como indicativas de la composición relativa de AAm y el AAc en estos materiales. La capacidad de hinchamiento en equilibrio de los terpolímeros (QUI/PAAc/PAAm) resultó altamente dependiente de la composición. Al ser sometidos a un tratamiento con NaOH(ac) 1 mol/L las características del sistema variaron apreciablemente. Se incrementó el hinchamiento y la sensibilidad al pH del medio en comparación con los sistemas QUI/PAAc/PAAm antes del tratamiento con NaOH(ac). Estos resultados fueron discutidos en términos de los cambios químicos y estructurales que tienen lugar durante el tratamiento con NaOH(ac). Los geles son denominados “sistemas inteligentes” por ser sensibles a la temperatura y la fuerza iónica del medio

Acemannan Gels and Aerogels

The procedures to obtain two types of acemannan (AC) physical gels and their respective aerogels are reported. The gelation was induced by the diffusion of an alkali or a non-solvent, then supercritical CO2 drying technology was used to remove the solvent out and generate the AC aerogels. Fourier-transform infrared spectroscopic analysis indicated that alkali diffusion produced extensive AC deacetylation. Conversely, the non-solvent treatment did not affect the chemical structure of AC. Both types of gels showed syneresis and the drying process induced further volume reduction. Both aerogels were mesoporous nanostructured materials with pore sizes up to 6.4 nm and specific surface areas over 370 m2/g. The AC physical gels and aerogels enable numerous possibilities of applications, joining the unique features of these materials with the functional and bioactive properties of the AC

Study of the Thermal Phase Transition of Poly(N,N-diethylacrylamide-co-N-ethylacrylamide) Random Copolymers in Aqueous Solution

N-alkyl-substituted polyacrylamides exhibit a thermal coil-to-globule transition in aqueous solution driven by an increase in hydrophobic interactions with rising temperature. With the aim of understanding the role of N-alkyl substituents in the thermal transition, this study focuses on the molecular interactions underlying the phase transition of poly(N,N-diethylacrylamide-co-N-ethylacrylamide) random copolymers. Poly(N,N-diethylacrylamide) (PDEAm), poly(N-ethylacrylamide) (PNEAm), and their random copolymers were synthesized by free radical polymerization and their chemical structure characterized spectroscopically. It was found that the values of the cloud-point temperature increased with PNEAm content, and particle aggregation processes took place, increasing the negative charge density on their surface. The cloud-point temperature of each copolymer decreased with respect to the theoretical values calculated assuming an absence of interactions. It is attributed to the formation of intra- and interchain hydrogen bonding in aqueous solutions. These interactions favor the formation of more hydrophobic macromolecular segments, thereby promoting the cooperative nature of the transition. These results definitively reveal the dominant mechanism occurring during the phase transition in the aqueous solutions of these copolymers

Preparation methods of chitosan nanoparticles: a review

El quitosano es un polisacárido natural que ha sido utilizado frecuentemente en el desarrollo de distintos materiales, debido a sus excepcionales propiedades fisicoquímicas y biológicas. Las nanopartículas de quitosano son generalmente producidas por estrategias denominadas de construcción (del inglés “bottom up”), donde el ensamblado polimérico es promovido por distintas interacciones moleculares. Sin embargo, un grupo de estrategias llamadas de deconstrucción (del inglés “top-down”) basadas en la fragmentación de estructuras macroscópicas, han generado un gran interés recientemente como alternativa para la obtención de nanomateriales. El presente trabajo hace una revisión bibliográfica de los resultados obtenidos por distintas investigaciones sobre la producción de sistemas de nanopartículas basadas en quitosano durante las últimas décadas. Las evidencias demostraron que las nanopartículas de quitosano juegan un papel preponderante en la investigación de los nanomateriales poliméricos con aplicaciones biomédicas y farmacéuticas, debido a la gran diversidad de métodos de obtención existentes que determinan las propiedades de los materiales, tales como tamaño de partícula, capacidad de incorporación y liberación de compuestos bioactivos, carga superficial, mucoadhesividad, entre otras

Mesoscopic Modeling of the Encapsulation of Capsaicin by Lecithin/Chitosan Liposomal Nanoparticles

The transport of hydrophobic drugs in the human body exhibits complications due to the low solubility of these compounds. With the purpose of enhancing the bioavailability and biodistribution of such drugs, recent studies have reported the use of amphiphilic molecules, such as phospholipids, for the synthesis of nanoparticles or nanocapsules. Given that phospholipids can self-assemble in liposomes or micellar structures, they are ideal candidates to function as vehicles of hydrophobic molecules. In this work, we report mesoscopic simulations of nanoliposomes, constituted by lecithin and coated with a shell of chitosan. The stability of such structures and the efficiency of the encapsulation of capsaicin, as well as the internal and superficial distribution of capsaicin and chitosan inside the nanoliposome, were analyzed. The characterization of the system was carried out through density maps and the potentials of mean force for the lecithin-capsaicin, lecithin-chitosan, and capsaicin-chitosan interactions. The results of these simulations show that chitosan is deposited on the surface of the nanoliposome, as has been reported in some experimental works. It was also observed that a nanoliposome of approximately 18 nm in diameter is stable during the simulation. The deposition behavior was found to be influenced by a pattern of N-acetylation of chitosan

Chitosan Based Polyelectrolyte Complexes as Potential Carrier Materials in Drug Delivery Systems

Chitosan has been the subject of interest for its use as a polymeric drug carrier material in dosage form design due to its appealing properties such as biocompatibility, biodegradability, low toxicity and relatively low production cost from abundant natural sources. However, one drawback of using this natural polysaccharide in modified release dosage forms for oral administration is its fast dissolution rate in the stomach. Since chitosan is positively charged at low pH values (below its pKa value), it spontaneously associates with negatively charged polyions in solution to form polyelectrolyte complexes. These chitosan based polyelectrolyte complexes exhibit favourable physicochemical properties with preservation of chitosan’s biocompatible characteristics. These complexes are therefore good candidate excipient materials for the design of different types of dosage forms. It is the aim of this review to describe complexation of chitosan with selected natural and synthetic polyanions and to indicate some of the factors that influence the formation and stability of these polyelectrolyte complexes. Furthermore, recent investigations into the use of these complexes as excipients in drug delivery systems such as nano- and microparticles, beads, fibers, sponges and matrix type tablets are briefly described